Batch-type sludge drier

ABSTRACT

A drier having a boxlike housing (12) for receiving a hopper (13) therein which contains a batch of wet sludge. The hopper (13) cooperates with the housing, when closed therein, to define a closed air recirculation system which supplies dry pressurized warm air into an air-receiving chamber (79) located at the bottom of the hopper. The air passes upwardly through a perforated bottom wall (78) into and through the sludge to remove moisture therefrom. The moist air passes upwardly through the open top of the hopper, through a filter and is supplied to a drying unit (34) located in the housing for removing moisture therefrom, which moisture is externally discharged. The drying unit resupplies the dry air back to the drying chamber formed in the hopper.

FIELD OF THE INVENTION

This invention relates to an improved batch-type drying apparatus forwet materials and particularly sludgelike materials.

BACKGROUND OF THE INVENTION

Numerous apparatus have been developed for drying wet sludgelikematerials, such as metal hydroxide sludge as generated in platingoperations and the like. Such apparatus, of both the batch andcontinuous type, often employ heaters and/or agitators to reduce thedrying time as a heating fluid, normally air, is circulatedtherethrough. While these known apparatus have operated in a reasonablysatisfactory manner, nevertheless there is an ongoing need forimprovements in such drying apparatus which improve operationalefficiency and reduce operating costs, and/or increase the amount ofmoisture which can be efficiently removed from the sludgelike material.

In one known apparatus, as disclosed in German Gebrauchsmuster No.G9100341.5, the sludge drying apparatus is of the batch-type andutilizes a closable boxlike housing in which a wheeled hopper containinga batch of sludge can be positioned. The housing contains arefrigeration-type air drying apparatus which defines a closedrecirculating air system for supplying dry air into the bottom of thehopper so that the air is fed upwardly through the sludge to removemoisture therefrom, with the wet air being dried and then resupplied tothe drying apparatus for removing moisture therefrom. The air iscontained in a closed recirculating system while permitting reasonablyefficient removal of moisture therefrom, and hence removal of moisturefrom the sludge to permit drying thereof.

In the aforementioned apparatus, however, numerous structural andoperational features are present which make both construction and use ofthis apparatus less than optimum. For example, the hopper has anoperable front door to assist in removing the dried material when thehopper is removed from the apparatus, although it has been discoveredthat unloading of the material nevertheless still often requires manualshoveling of the material from the drying chamber for discharge throughthe front door. Further, in this known apparatus some of the driedmaterial tends to fall through the perforated floor plate into the airsupply chamber, and such material can be removed from the air supplychamber only by manually removing it through the air supply opening asformed in the back wall of the hopper. This known apparatus also lacksadequate controls for safe and automatic operation of the apparatus, andfor example requires that the drying apparatus be defrosted by means ofa manually-controlled switch.

Accordingly, it is an object of this invention to provide an improvedbatch-type drier, particularly for drying sludge such as filter cake,which improved drier overcomes many of the disadvantages associated withthe drier described above.

More specifically, the improved drier includes a boxlike housing forreceiving a hopper therein which contains a batch of wet sludge. Thehopper cooperates with the housing, when closed therein, to define aclosed air recirculation system which supplies dry pressurized warm airinto a small air-receiving chamber located at the bottom of the hopper.The air passes upwardly through a perforated bottom wall into andthrough the sludge to remove moisture therefrom. The moist air passesupwardly through the open top of the hopper, through a filter and issupplied to a drying unit located in the housing for removing moisturetherefrom, which moisture is externally discharged. The drying unitresupplies the dry air back to the drying chamber formed in the hopper.The air remains captivated and is recirculated to prevent escape ofundesired volatiles, but significant moisture is nevertheless removedand externally discharged so as to permit efficient drying of the sludgewithout use of a separate heater.

In this improved drier, the sludge is deposited in the hopper throughthe upper top thereof, and is also discharge therefrom by tipping of thehopper after the sludge has been dried. For this purpose, the hopper hassupporting structure associated with the bottom thereof foraccommodating the tines or lifting elements of a conventional forklifttruck. The supporting structure is normally rigidly coupled to thebottom of the hopper through a releasable latch. This supportingstructure, when unlatched, permits relative vertical tilting of thehopper with respect to the supporting structure, which tilting isconstrained to a limited angular extent by a restraining structureassociated with the supporting structure. This arrangement enables thehopper containing the dried material to be attached to the lift fork andraised upwardly and then tilted over a receiving container so that thedried material can be dumped from the hopper through a discharge openingin the back wall thereof. This simultaneously permits any dried materialwhich has fallen into the drying chamber to move toward and bedischarged outwardly through the air supply opening so as to permitdumping of material from the drying chamber automatically andsimultaneous with dumping of the material from the main drying chamber.

In this improved drier, as aforesaid, the perforated bottom wall of thedrying chamber can be generally flat and spaced only a small distancefrom the bottom wall of the air supply chamber, thereby maximizing thecapacity of the sludge-receiving drying chamber.

The improved drier, as aforesaid, also incorporates automatic controlswhich permit actuation of the overall apparatus only when the hopper isproperly positioned and latched within the housing and the doors closedso as to then permit operation of the air recirculation and dryingsystem. The drying system also incorporates an automatic defrost cycleand sensor which automatically initiates defrosting when such isrequired to hence optimize efficient operation of the system.

The improved drier, as aforesaid, also incorporates improvements in theair drying system to optimize the condensation of moisture from the airafter passing through the hopper, and the efficient operation of therefrigeration part of the drying system.

Other desirable structural and operational features of the presentinvention will be apparent to persons familiar with structures of thisgeneral type upon reading the following specification and inspecting theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of the drier according to the presentinvention, and showing the upper front wall partially broken away andthe doors in an open position.

FIG. 2 is a left side elevational view with an upper portion of the sidewall removed to show interior components.

FIG. 3 is a top plan view with the top wall removed.

FIG. 4 is a diagram of the refrigeration system provided for drying theair.

FIG. 5 is a side view of the hopper or hopper.

FIG. 6 is a fragmentary top view of the hopper.

FIG. 7 is a rear elevational view of the hopper.

FIG. 8 is fragmentary front elevational view of the hopper.

FIG. 9 is a fragmentary front view similar to FIG. 8 but illustrating amodified but preferred variation of the latch between the hopper andtilt structures.

FIG. 10 illustrates the mounting and dumping of the hopper by aforklift.

Certain terminology will be used in the following description forconvenience in reference only, and will not be limiting. For example,the words "upwardly", "downwardly", "rightwardly" and "leftwardly" willrefer to directions in the drawings to which reference is made. The word"front" will refer to the side of the drier which is provided with doorsand through which the hopper is moved, and the word "back" will refer tothe opposite side of the drier. The words "inwardly" and "outwardly"will refer to directions toward and away from, respectively, thegeometric center of the drier and designated parts thereof. Saidterminology will include the words specifically mentioned, derivativesthereof, and words of similar import.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, there is illustrated a batch-type drier 11according to the present invention. This drier includes a generallyhollow boxlike housing 12 adapted to have a roller-supported hopper 13positioned therein, which hopper contains therein a batch of sludge. Anair drying and circulating system 14 is associated with the housing, andis disposed primarily in the upper portion thereof, for circulating airthrough the hopper to remove moisture from the sludge, with the wet airbeing circulated back through the system 14 to effect removal of thewater therefrom so that the dried air can then be resupplied to thehopper.

The housing 12 includes upper and lower housing portions 16 and 17,respectively, both of which are of a closed but hollow boxlikeconfiguration. These housing portions 16 and 17 are of generallyrectangular horizontal cross section and are defined by opposed andgenerally parallel upright side walls 18 and 19 which are rigidly joinedby a back or rear wall 21. The upper housing portion 16 also has a frontwall 22 which rigidly extends between the side walls and is generallyparallel with the rear wall 21. The front side of the lower housingportion 16 defines an enlarged opening 23 which provides communicationwith an interior drying chamber 24 as defined within the lower housingportion 17. The opening 23 can be closed by a pair of doors 25 swingableabout hinges 26 which couple the door edges to the housing adjacent thefront edges of the opposite side walls. The doors can be closed andlatched by a conventional handle and latch mechanism as provided on oneor both doors. The doors, when closed, effectively seal off the interiordrying chamber 24 from the surrounding environment.

The housing also includes top and bottom walls 27 and 28, respectively,which bottom wall is adapted to be positioned in supportive engagementwith a floor or the like. A substantially horizontally extendingintermediate wall 29 extends across the hollow interior of the housingsubstantially midway between the top and bottom walls thereof so as toeffectively close off the drying chamber 24 defined in the lower housingportion 17 and thus separate it from the interior of the upper housingportion 16.

The upper housing portion 16 has a vertical divider wall 31 whichfixedly extends between the top and intermediate walls, and the opposedside walls, and divides the interior of housing portion 16 into firstand second side-by-side compartments 32 and 33, respectively. The firstcompartment 32 functions as a wet air chamber, whereas the secondcompartment 33 is an ambient air chamber. Different parts or componentsof the air drying and circulation system 14 are disposed in thesechambers 32 and 33, as described below.

Positioned within the first chamber 32, as indicated by FIG. 2, is acoil-type evaporator 34 which is positioned adjacent but spaced slightlyrearwardly from the front wall of the housing. This evaporator extendstransversely across the chamber 32, and the coils thereof are providedwith fins to improve heat transfer efficiency. In the region between theevaporator 34 and the front wall 22, there is provided an opening 35formed in the intermediate wall 29 to provide communication with anupper part of the drying chamber 24. The moist air from drying chamber24 passes upwardly through opening 35 into the upstream end of chamber32 and thence through the evaporator 34 to effect condensation of muchof the moisture carried by the air. The condensed moisture, namelywater, collects in a generally V-shaped trough or reservoir 36 formedbelow the evaporator, and this reservoir communicates with a conduit 37which provides discharge of the water to an external collecting device.

Positioned downstream of the evaporator 34, and disposed so as to extendtransversely across the chamber 32, is a coil-type condenser 38, thelatter including multiple coils positioned closely adjacent and in linewith one another so that the air discharged from the evaporator 34sequentially passes over the condenser coils. The air leaving thecondenser 38 passes into a collection region or space 41 located at therearward end of chamber 32, which region 41 communicates with the inletof a fan or blower unit 42 as mounted in the ambient chamber 33.

The blower unit 42 (preferably a centrifugal compressor) includes adrive motor 43 which drives a conventional blower or fan wheel (notshown) as disposed within a shroud or housing 44, which housing 44 hasan air inlet 45 which opens through the divider wall 31 forcommunication with the air in the collection region 41. The blower unit42 has a pressurized air discharge 46 which connects to an opening inthe intermediate wall 29 for direct communication with the upper end ofan air duct 47 which is fixed to the rear wall 21 and projectsvertically downwardly through the interior of the drying chamber 24.This duct 47, at its lower end as positioned close to but slightly abovethe floor of the housing, is provided with a ringlike rectangular collar48 which projects forwardly a small extent and terminates in a largeforwardly-directed discharge opening 49. This opening 49 is provided soas to discharge pressurized dry air into the bottom of the hopper 13when the latter is positioned in the drying chamber 24, as explainedhereinafter.

The ambient chamber 33 also has a further coil-type condenser 51positioned therein, the latter being disposed closely adjacent andextending generally across an opening formed in the adjacent side wall18, which opening is covered by a suitable grid or mesh 52. Ambient aircan flow through this opening and across the condenser 51 into thechamber 33 whenever a suction fan 53 as mounted in the top wall 27 isactivated. The suction fan 53 discharges outwardly through the top wall.

The ambient chamber 33 also mounts therein other components associatedwith the drying and circulating system 14 including, as illustrated inFIG. 3, a compressor 54 for the refrigerant used in the drying system,an accumulator 55 for refrigerant, and a storage or receiving tank 56for refrigerant.

The system 14 also includes a portion of the refrigerant line formedinto a serpentine heat exchanger 57 which is positioned within chamber32 directly between the evaporator 34 and the condenser 38. This heatexchanger 57 extends transversely across the chamber so as to becontacted by the airstream as it flows from evaporator 34 to condenser38.

Chamber 32 also has a humidistat 59 mounted therein upstream of theevaporator 32, which humidistat is preferably positioned in generalalignment with and in close proximity to the communication opening 35 soas to sense the humidity of the air as it is discharged from the dryingchamber 24.

The refrigeration cycle employed in the drying system 14, asdiagrammatically illustrated by FIG. 4, includes a main line or conduit61 through which the refrigerant passes and which couples the variouscomponents of the system so as to define a closed-loop arrangement. Thisconduit 61 includes portions thereof which are coiled in serpentine formso as to define the evaporator 34 and the condensers 38 and 51.

As indicated by FIG. 4, the refrigerant discharged from compressor 54 isinitially supplied to the primary condenser 38 while the refrigerant isat its highest temperature, and thereafter passes through the secondarycondenser 51. The refrigerant line 61 after leaving the secondarycondenser is then coiled so as to create an auxiliary condenser or heatexchanger 57 which is positioned downstream of the evaporator 34. Fromthis point the refrigerant line 61 has a refrigerant sight glass 62 anda refrigerant drier 63 coupled thereto. The refrigerant line thenconnects to an expansion valve 64 located just upstream of theevaporator 32. From the evaporator 34 the refrigerant is supplied to theaccumulator 55 and thence back to the intake or low pressure side of thecompressor 54. A pressure switch 65 is coupled between the input andoutput of the compressor for sensing the pressure differential andcontrolling operation of the compressor. Another refrigerant pressureswitch 66 senses the pressure (and hence indirectly the temperature) ofthe refrigerant in the supply line to the condenser 38, which switch isactivated to turn on the fan 53 and hence activate the secondarycondenser 51 when the pressure sensed by switch 66 increases so as toindicate a warming of the refrigerant.

Considering now the structure of the hopper 13, and referring to FIGS.5-8, hopper 13 has a generally upwardly-opening boxlike configuration inthat it includes generally parallel upright front and rear walls 71 and72 which are rigidly joined together by generally parallel side walls 73and 74 which extend perpendicularly between the front and rear walls.The walls 71-74 are secured to and project upwardly with respect to agenerally horizontally extending base wall 75. The top 76 of the hopperis open. The hopper defines therein a material-receiving chamber 77which projects downwardly from the open top 76 and terminates at a floor78. This floor 78 extend substantially horizontally across the hopperand is spaced upwardly from the bottom or base 75 by only a smalldistance, such as in the order of about five inches. This small verticalspacing between the base 75 and floor 78 defines an air-receivingchamber 79 which is located below the material-receiving chamber 77. Thefloor 78 contains perforations which, in the illustrated embodiment,comprise narrow slots 81 which extend across the width of the floor topermit air to pass upwardly into the material contained in the chamber77. The floor is also preferably provided with angled plates ordeflectors 82 which slope upwardly over the slots 81 and projectgenerally toward the rear wall of the hopper so as to minimize passageof solid material downwardly through the slots.

The hopper is provided with a pair of conventional cylindrical rollers83 secured to the base adjacent the rear corners thereof, and similarswivel-type rollers or casters 84 are secured to the base adjacent thefront corners of the hopper.

The rear wall 72 of the hopper has a large discharge opening 85 formedtherein, which discharge opening extends across substantially the fullwidth of the hopper and has a lower edge defined in close proximity tothe elevation of the slotted floor 78. A door 86 is secured by ahorizontal hinge 87 along its upper edge to the rear wall 72 at alocation spaced a small distance downwardly from the top edge of thehopper. This door 86 is positioned to overlap the discharge opening 85by abutting the rear wall so as to close off the discharge opening. Tohold the door 86 in a closed position, manually releasable latches 88are provided adjacent the lower corners of the door. Each latch 88includes a latch lever 89 which is positioned adjacent the respectiveside wall 73 or 74 and is hingedly supported therein by a hinge pin 91.The latch lever 89, adjacent the free end thereof, is provided with alatching hook 92 which projects outwardly and is gravity-urgeddownwardly for latching engagement with a stublike latch pin 93 which isfixed to and projects sidewardly from the adjacent lower corner of thedoor 86. The latch 88, when engaged as illustrated by FIG. 5, preventsopening of the door 86 and permits such opening only after the latch hasbeen manually released by swinging the latch hook counterclockwise aboutthe pivot 91. The free end of the latching hook 92 is provided with acamming surface 94 thereon which is engaged by the latch pin 93 when thedoor swings toward its closed position so that the latch pin camminglyengages the latch lever and swings it upwardly to enable full closure ofthe door, following which the latch lever swings downwardly by gravityto latchingly engage the latch pin.

The rear wall 72 of the hopper also has an air inlet opening 95 formedtherethrough for direct communication with the air chamber 79. This airinlet opening 95 is positioned below the material discharge opening 85,as indicated by FIG. 8, and is adapted to substantially align with anddirectly communicate with the air discharge opening 49 defined at thebottom of the air supply duct 47. Air inlet opening 95 also functions topermit discharge of dried material which falls into the air chamber 79,as explained hereinafter.

To facilitate handling and emptying of the hopper 13 when it is removedfrom the drier, the hopper is provided with a lifting and tiltingstructure 110 secured to the underside thereof. This structure 110includes a pivotal support platform 111 positioned under the base walland defined by a generally horizontally extending base plate 112 havinga pair of generally parallel channels 113 fixedly secured thereto insidewardly spaced relationship. The channels 113 are secured in invertedfashion to the upper side of the base plate 112 to define a pair ofgenerally parallel and sidewardly space tunnels which project under thehopper, with the sideward spacing of these tunnels corresponding to theconventional sideward spacing between the two tines associated with aconventional lift fork of a lift truck.

The channels 113, adjacent the ends thereof which are disposed in closeproximity to the front side of the hopper, are also rigidly secured by across plate which extends between and is joined to the upper surfacesthereof. This cross plate also supportingly abuts the underside of thehopper when in the normal stored and latched position illustrated byFIG. 5. The inner or rearward ends of the channels 113 terminate closeto the central vertical plane 114 of the hopper and are pivotallycoupled to the hopper by hinge pins 115 which couple to brackets 116secured to the underside of the hopper bottom wall. These hinge pinsdefine a substantially horizontal hinge axis 117 which projectssidewardly of the hopper in generally parallel relationship to the frontand rear walls thereof, and is spaced a small distance forwardly fromthe central vertical plane 114. This hinge axis 117 is disposed on theopposite side of the vertical plane 114 from the discharge opening 85,which results in this hinge axis being positioned horizontally on theopposite side of the center of gravity of the hopper relative to thedischarge opening.

To rigidly and non-swingably secure the platform 11 to the hopper, thereis provided a latch arrangement 118 which is disposed adjacent the frontlower edge of the hopper for cooperation with the platform. This latcharrangement includes a latch lever 119 which is pivotally mounted abouta pivot 121 to the front end of the platform. This latch lever has ahook 122 on the upper end thereof adapted for latching engagement with ashoulder 123 which is fixed to the front wall of the hopper. The latchlever 119 is gravity urged into the latched position illustrated, withthe latch being manually swingable for permitting release thereof.

Referring now to FIG. 9, there is illustrated a preferred variation ofthe latch structure 118' for fixedly but releasably securing theplatform 112 to the hopper 13. This modified latch 118' includes a latchmember 119' formed as an elongate pin and slidably supported on abracket 141 fixed to one of the channels 113 adjacent the front wall ofthe hopper. This pin 119' is slidably urged, as by a spring 142 whichconcentrically surrounds the latch pin, toward a latching positionwherein the projecting free end of the latch pin projects through anopening formed in a latch stop or abutment 123' which is fixedly securedto the front wall 71 of the hopper adjacent the lower edge thereof. Thelatch pin has a loop 143 secured to the other end thereof, which loop inturn has a pull cable or rope (not shown) connected thereto so that anoperator can axially pull the latch pin outwardly (rightwardly in FIG.9) to disengage the latch pin from the abutment and hence release thehopper for pivotal movement relative to the support platform.

The platform 111 is also interconnected to the hopper by a restrainingstructure for permitting vertical pivotal movement of the platform 111relative to the hopper 13 through only a small angular extent, whichangular extent is preferably a maximum in the range of about 35° toabout 45°. This restraining structure includes an elongate flexiblerestraining element 124, such as a heavy cable (i.e. a nylon strap) orchain. This restraining element 124 has one end thereof coupled to abracket 125 secured to the underside of the hopper, and the other endcoupled to a further bracket 126 which is secured to the platform 111intermediate the ends thereof. This restraining element 124 limitsrelative pivotal movement between the hopper and platform to a maximumangle as diagrammatically illustrated by FIG. 10.

To secure the platform 111 to a forklift truck when transporting oremptying of the hopper is desired, the hopper 13 also is provided withan anchoring structure for connection between the hopper and forklift.As illustrated by FIG. 10, there is provision for an elongate flexibleanchoring element 128 such as a chain or cable, and one end of thisanchoring element is secured to a fixed anchor 127 provided on the outeror front end of the platform 111 substantially at the midpoint thereof.The other end of this flexible anchor element 128 has a conventionalhook or fastener 129 thereon and this latter anchor is used to engageone of the transverse support elements which is conventionally providedon and extends between the vertical supports of the forklift arrangementF.

To facilitate proper and safe operation of the drier of the presentinvention, the bottom wall of the drier is provided with a pair ofgenerally parallel and sidewardly spaced guide rails 131 fixed to andprojecting upwardly therefrom, which guide rails projects in thefront-to-back direction so as to closely confine and guide the hoppersupport rollers therebetween. This ensures that the hopper is properlyaligned when moved into the drying chamber so as to ensure that the airdischarge on the rear duct is properly aligned with the air inletdefined in the rear wall of the hopper.

Further, when the hopper 13 is positioned in the drying chamber 24, itis moved rearwardly until the collar 48 defining the air dischargeopening 49 substantially abuts the rear wall 72 of the hopper, therebyensuring proper communication of the openings 49 and 95. This is furtherensured by the provision of the hopper positioning latches 132 asprovided on the front side of the housing directly inside the doors 25.These latches 132 are positioned adjacent the opposite front edges ofthe housing and are supported thereon by pivots 133, and are accessibleonly when the doors are open. The latch levers are normally stored in anupright position when the hopper is moved into or out of the dryingchamber. After the hopper has been moved into the drying chamber, thenthese latch levers 132 are manually swung downwardly into a generallyhorizontal position, as limited by stops 134, so that the latch leversproject over and are positioned closely adjacent the front wall of thehopper. These latch levers prevent outward movement of the hopperrelative to the drying chamber. Further, these latch levers can bepivotally swung downwardly into the latching position only if the hopperis properly positioned in the drying chamber so as to ensure that theinlet opening 95 in the hopper is substantially abuttingly engaged withthe outlet opening 49 in the air supply duct 47.

The drier 11 is also provided with a safety switch 135 mounted on thehousing, specifically on one of the fixed frame elements closelyadjacent the upper edge of the door opening. This safety switch isdeactivated whenever the doors are open, and is contacted by the doorand activated only when the door is closed. This safety switch, whenactivated, permits the drying cycle to be initiated.

The drier is provided with a control panel (not shown) thereon foraccess and visual observation by an operator. This control panelpreferably includes a three-position selector switch which includes an"off" position, a "manual" position for permitting manual control overthe cyclic operation, and an "auto" position for permitting automaticpreset control of the drying cycle. The control panel also preferablyincludes a programmable timer which permits setting of a predeterminedcycle time and which shows elapsed cycle time, a programmable humidistatwhich permit setting of the predetermined dryness of the sludge forterminating the end of an automated drying cycle, and a conventionalmanually-operated "start" switch.

The control selection for the drying cycle involves the operatoractivating the selector switch to select the "manual" mode, then settingthe timer for the desired length of time of the drying cycle (forexample, 20 hours), and then activating the "start" switch. The timershuts off the machine when its time is out.

Alternately, if the operator selects the "auto" mode, then the operatoradjusts the humidistat control to select the desired final moisture orhumidity of the sludge (for example, 20% relative humidity), andthereafter activates the "start" switch. The machine will continue torun until the humidity of the wet air, as sensed by the humidistat,reaches the preset value, at which time the machine shuts off.Operation:

The operation of the drier according to the present invention will nowbe briefly described to ensure a complete understanding thereof.

To initiate a drying operation, a load of wet sludge (i.e. filter cake)is positioned within the chamber 77 of the hopper 13, and the hopper isthen rollingly moved into the drying chamber 24, preferably with theassistance of a forklift truck. When the hopper is positioned so thatthe duct outlet 49 is aligned with the air inlet opening 95 formed inthe lower portion of the hopper rear wall, then an operator swings thelatch levers 132 downwardly to overlap the front wall of the hopper, andthen closes the doors 25 which activates the safety switch 135 so thatthe drier is thus in a position to be operated.

The operator then pushes or activates the manual start switch (notshown) which activates the air drying and circulating system 14.

The blower unit 42 is activated which discharges pressurized, dry warmair into the duct 47 where it is discharged through the opening 49 intothe air chamber 79 defined at the bottom of the hopper. The air inchamber 79 then flows upwardly through slots 81 and upwardly through thewet sludge. Since the sludge is wet and at a temperature below that ofthe air, the air flowing upwardly through the sludge effectsvaporization of moisture from the sludge so as to cause partial dryingand warming of the sludge, with the moist but now cooler air flowingupwardly through the open top of the hopper so as to be sucked upwardlythrough the opening 35 into the front portion of the wet air chamber 32.At this location, the humidistat 59 senses the humidity of the wet airleaving the sludge. The wet air then flows horizontally rearwardly ofthe wet air chamber 32 and, in doing so, first passes through the airfilter 58 and evaporator 34, then over the heat exchanger 57, and thenthrough the condenser 38 into the collection space 41. In passing overthe evaporator 34, the moisture in the air condenses on the coils so asto effect drying and cooling of the air, and simultaneously the latentheat of condensation is released and hence effects warming of therefrigerant as it flows through the evaporator. The dry air then passesover the condenser 38 and is heated. The air reaching the collectionspace 41 is thus warmer and drier then the air entering the wet airchamber 32 through the inlet opening 35. The air in space 41 is thensucked into the inlet 45 of the blower unit 42 which pressurizes the airand resupplies it back into the duct 47 for recirculation.

The moisture which condenses on the coils of the evaporator 34 flowsdownwardly and collects in the water collection trough or reservoir 36for discharging externally of the drier.

In operation of the drier as briefly summarized above, the compressor 54is energized and initially supplies the refrigerant through the line 61to the coils of the main condenser 38, with the refrigerant thereafterbeing supplied to the secondary condenser 51. The refrigerant leavingthe secondary condenser 51 then flows through the auxiliary condenser orheat exchanger 57, and then passes through the expansion valve 64 so asto be supplied into and through the evaporator 34 and then back to thecompressor.

During the initial phase of the drying cycle, the sludge is of lowesttemperature and highest moisture content, and during this initial phaseof operation the refrigerant tends to remain at a lower temperature andpressure, and effective heat exchange across solely the main condenser38 is sufficient to maintain proper operation of the system. However,during the later phase of the drying cycle, due to gradual warming ofthe sludge and reduction in the moisture content, the air supplied tothe wet air chamber 32 is of slightly higher temperature and lessmoisture content, and the condenser 38 may by itself be insufficient tomaintain the refrigerant at desired temperature and pressure. Thus, ifthe pressure in the refrigerant line 61 reaches a predetermined maximumso as to indicate a predetermined maximum refrigerant temperature, thenthe switch 66 activates the fan 53 which sucks warmer ambient airthrough the grid or opening 52 and across the condenser 51 which causescondensation of the refrigerant and removal of heat from the refrigerantso as to cause additional cooling thereof to maintain the refrigerant atthe desired operating pressure and temperature. This secondary condenser51 is activated, namely activated by the pressure switch 66 activatingthe fan 53, only as necessary when demanded by the refrigeranttemperature in the system so as to maintain proper operation. During amajority of the drying cycle, the secondary condenser 51 is notactivated.

Further, if the condensation deposited on the evaporator 34 creates afrost or freezing problem, then such will be sensed by a reduction inthe pressure between the inlet and outlet to the compressor 54, assensed by the pressure switch 65. When this switch 65 senses a minimalpressure differential, then the switch shuts off the compressor 54 toallow the air flow over the evaporator to melt the frost or ice. Thecompressor 54 will restart when the pressure switch 65 senses that therefrigerant temperature has again exceeded a predetermined minimum.

The provision of the auxiliary condenser coil 57 in the system, andparticularly its connection in the refrigerant pipe 61 directly upstreamof the evaporator 34 with respect to refrigerant flow, but its positiondownstream of the evaporator 34 with respect to airflow, is highlydesirable for providing increased refrigerating effect in the system.This coil 57, due to its physical position for contact with the cold airdirectly downstream of the evaporator 34, functions to cool the liquidrefrigerant within the line 61 at a location directly upstream of theexpansion valve 64. This provides increased cooling of the refrigerantand improves the overall efficiency of the system, and at the same timereduces and limits the amount of time that the auxiliary fan 53 ofsecondary condenser 51 must be activated.

While the overall drying cycle will require a significant numbers ofhours, nevertheless such drying is effective in highly reducing themoisture content of the sludge, and for example can result in the driedsludge having a density which is a small fraction of the density of theinitial wet sludge. Since disposal costs are often associated withweight, the ultimate cost of disposing of the dry sludge issignificantly reduced.

After the drying cycle has been completed, the doors of the housing areopened, the latch levers 132 swung upwardly, and the hopper 13 removedfrom the drying chamber.

To assist in removal of the hopper, a conventional forklift can beutilized. The forklift can be positioned so that the fork F ispositioned in a lowered position close to the ground so that the pair offorwardly projecting fork elements project forwardly and are alignedwith the tunnels defined by the channels 113. The fork elements can thenbe inserted into the tunnels until the ends thereof substantially abutthe hinge pins 115. At such time the aforementioned provision allows theflexible anchor element 128 is then stretched rearwardly and the hook129 thereof engaged over the transverse support on the fork mechanism.The lift truck can then move rearwardly and pull the hopper 13 out ofthe housing. The fork mechanism can then be raised a small extent so asto raise the hopper upwardly, following which the hopper can betransported to a desired location for dumping, such as to a collectingbin.

When dumping of the hopper is desired, the hopper can be elevated to adesired elevation so that the rear portion of the hopper is positionedover a collecting bin. The door latches 88 are manually released so asto permit opening of the discharge door 86. Thereafter the latch 118 or118' is manually released. For this purpose, the latch member 119 or119' is normally provided with a pull cable (not shown) attached theretoso as to permit an operator to release the latch 118 or 118' whileremaining somewhat spaced from the hopper. As soon as this latch 118 or118' is released, then the hopper immediately pivots into a dumpingposition (see FIG. 10) about the hinge axis 117 due to the latter axisbeing disposed in spaced relationship and forwardly from the centralvertical plane 114 of the hopper. The hopper pivots about axis 117 intoan orientation wherein the bottom wall is inclined at an angle of about40° relative to the horizontal, such angle being restrained by theflexible restraining element 124 coupled between the bottom wall of thehopper and the support platform 111. Further, since the support platform111 is preferably coupled to the forklift by the anchor element 128, thehopper can be prevented from falling off of the forklift. As the hopperpivots into the dumping position illustrated by FIG. 10, this alsocauses the rear door 86 to swing outwardly away from the rear wall 72 soas to hang in a downward pendant position, whereupon the dried materialin the sludge chamber 77 slides downwardly along the floor 78 and isdischarge outwardly through the rear discharge opening 85. Due to themanner in which the deflectors 82 angle upwardly over the slots 81 inthe rearward direction, this tends to prevent the material from passingdownwardly through the slots, and facilitates the rear discharge of thematerial through the rear opening 85.

Simultaneous with the discharge of material through the main dischargeopening 85, any material which has fallen down into the drying chamber79 also slides rearwardly on the floor 78 thereof due to the inclinationof the floor, with the material in the air chamber 79 being free to flowoutwardly through the air inlet opening 95 which is disposed directlybelow the main discharge opening 85. This arrangement thus permits anymaterial which accidentally collects in the air chamber 79 to besimultaneously discharged along with the material from the main sludgechamber 77.

After the hopper has been completely dumped, then the forklift is movedrearwardly away from the collecting bin, and the fork lowered until therear wheels initially contact the floor. Further lowering of theforklift then result in the hopper being gradually pivoted downwardly soas to return to a horizontal position wherein all of the support wheelsare again supported on the floor. When reaching this latter position,the rear discharge door 86 has automatically swung back to its closedposition and, due to the action of the camming surfaces 94 on the latchpins 93, is effective in camming the latch levers 89 upwardly asufficient extent to enable the latch pins 93 to pass under andre-engage the latching hooks 92. The latch 118 or 118' between thesupport platform 111 and the front wall of the hopper is also re-engagedat this time. This re-engagement may be caused by springs whichcooperate with the latch lever 119 or 119', although the re-engagementis preferably assisted or positively checked by the operator to ensurethat the latch 118 or 118' is properly engaged.

The hopper is then in position to receive a further load of wet sludgetherein.

In the illustrated embodiment, the hopper is illustrated as having arectangular ringlike collar or extension 139 provided on the upper endthereof. This collar or extension is fixedly secured, as by means ofbolts, to the top of the hopper and permits provision of a hopper havingan increased sludge chamber capacity. This collar is provided when alarger capacity drier is required, with the collar being removed if asmaller capacity drier is desired.

A typical cycle of operation associated with drying a load of wetsludge, after the hopper has been sealed in the drying chamber, will nowbe briefly described.

Sludge or filter cake in the hopper will initially be of high moisturecontent, such as about 85% humidity, and at a temperature of about 75°F. After the control system is activated and reaches a steady stateoperation after initial start-up, with steady state is reached in aboutfive minutes, the pressurized air discharged into the bottom of thehopper will be at a temperature of about 110° F. As the air passesupwardly through the sludge, the air is cooled but at the same timepicks up a large amount of moisture and hence is effectively saturatedwith moisture. The moist air entering the wet chamber 32 may be at atemperature of about 75° F., whereas the surface temperature of theevaporator coil 34 may be about 32° F. The moist air in passing over theevaporator condenses on the coil and the latent heat of condensationreleased by the moisture significantly increases the temperature ofrefrigerant leaving the evaporator and effects cooling of the air, sothat the air leaving the evaporator may be about 60° F. This cool airthen immediately passes over the heat exchanger or auxiliary condensercoil 57, and the refrigerant within this coil is of a significantlyhigher temperature, such as about 80°, and hence the air effects coolingof the refrigerant to ensure that the refrigerant is liquified prior toits being resupplied to the expansion valve 64. The air then passes overthe coils of the condenser 38, which coils may have a surfacetemperature of about 115°. The air is significantly heated so that theair leaving the condenser 38 is at a temperature of about 110° F., whichair is then resupplied to the fan unit 42.

After the drying cycle has been in effect for a significant period oftime, such as in the order of about 16 hours, the relative humidity inthe filter cake may have been reduced to about 50%, and the filter caketemperature increased to about 85°. While the air entering into thefilter cake may still be in the order of 110° F., the air leaving thefilter cake and passing to the evaporator coil is now at a highertemperature of about 87° F., and typically will have a somewhat reducedmoisture content. Hence, somewhat reduced moisture condensation and heattransfer occurs across the evaporator 34 and the refrigerant temperaturewill begin to increase slightly. If the refrigerant temperature at thecondenser coils 38 reaches about 120° as sensed by sensor 66, then thefan unit 53 is turned on so as to activate the secondary condenser 51.This fan unit 53 draws ambient air at a temperature of about 80° F.across the condenser 51 so as to reduce the surface temperature of thecondenser 51 and reduce the temperature of the refrigerant therein backto an acceptable level. The fan 53 will be periodically activated onlywhen control of maximum refrigerant temperature is necessary. It hasbeen determined that this secondary condenser 51 will be activated onlywhen the moisture content in the filter cake has been significantlyreduced so that the air leaving the filter cake is of lower moisturecontent, such as occurs near the end of the drying cycle.

Although a particular preferred embodiment of the invention has beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In an apparatus fordrying a wet sludgelike material, said apparatus including confinementmeans (13) for containing a batch of said material, and a system (14)for supplying air through said batch of material for drying thematerial, said system including an air inlet (35) and an air outlet (49)communicating with said confinement means, said system comprising:amoist air chamber (32) communicating with said outlet (35) for receivingtherein moist air; fan means (42) for supplying pressurized dry air tosaid inlet (49), said fan means having an intake (45) in communicationwith said air chamber (32) at a location remote from said outlet (35);refrigeration means associated with said air chamber (32) for drying andheating the air as it flows therethrough from said outlet to saidintake; said refrigeration means including conduit means (61) forcontaining a flowable refrigerant therein, said conduit means (61)defining a closed loop flow path connected to a compressor (54) for therefrigerant; said conduit means (61) including a main condenser coil(38) connected in series with said compressor (54) downstream thereof, aheat exchanger coil (57) connected in series with said main condensercoil (38) downstream thereof, and an evaporator coil (34) connected inseries with said heat exchanger coil (57) downstream thereof, saidevaporator coil (34) being upstream of said compressor (54); saidevaporator and condenser coils (34,38) being disposed within andextending generally transversely across said air chamber (32) forcontact with the air moving therethrough, said condenser coil (38) beingpositioned downstream of said evaporator coil (34) relative to thedirection of air movement through said air chamber (32); said heatexchanger coil (57) being disposed within and extending transverselyacross said air chamber (32) at a location between said evaporator andcondenser coils relative to said air movement direction; and means (36)for collecting the water which condenses on the evaporator (34) forpermitting discharge thereof.
 2. An apparatus according to claim 1,wherein said conduit means (61) includes a secondary condenser coil (51)connected in series downstream of said main condenser coil (38) butupstream of said heat exchanger coil (57), said secondary condenser coil(51) being mounted outside of said air chamber (32) so as to be free ofcontact with the air which is recirculated through the sludgelikematerial, and auxiliary fan means (53) for causing flow of ambient airacross said secondary condenser coil (51).
 3. An apparatus according toclaim 2, including control means (66) for intermittently activating saidauxiliary fan means (53) in response to the refrigerant in the conduitmeans (61) exceeding a predetermined pressure or temperature.
 4. Anapparatus according to claim 2, including an ambient air chamber (33),said secondary condenser coil (51) and said fan means (42) being mountedin said ambient air chamber.
 5. An apparatus for batch drying of wetbulk material, comprising:a housing (12) defining therein a closed andsubstantially sealed drying chamber (24), said housing including a door(25) providing access to said drying chamber; a hopper (13) positionablewithin said drying chamber, said hopper including a boxlike structure(71-74) adapted to contain therein a batch of wet material to be dried;said boxlike structure including a bottom wall (75) and a generallytubular sidewall structure (71-74) fixed thereto and projecting upwardlytherefrom, and an intermediate floor (78) extending across said sidewallstructure at a small distance above said bottom wall (75) but downwardlya significant distance from an upper edge of said sidewall structure,said hopper defining therein a material-receiving chamber (77) disposedabove said floor (78) and an air chamber (79) defined between said floor(78) and said bottom wall (75), said floor having a plurality of smallopenings (81) extending therethrough for permitting passage of airupwardly from said air chamber into said material-receiving chamber;said sidewall structure including front and rear walls (71,72) rigidlyjoined together by left and right side walls (73,74), said rear wall(72) having a discharge opening (85) formed therein for directcommunication with said material-receiving chamber (77), said rear wallalso having an air supply opening (95) formed therethrough at a locationbelow said discharge opening (85) for direct communication with said airchamber (79), and door means (86) movably mounted on said boxlikestructure for normally closing said discharge opening (85); said hopperalso including a tilting structure (110) mounted to said boxlikestructure for permitting lifting of the hopper by a forklift andvertical tilting of the hopper about a substantially horizontal tiltaxis so that the rear wall of the hopper is vertically tilted downwardlyto permit simultaneous gravity-discharge of material through both thedischarge opening (85) and the air supply opening (95); said hopper alsoincluding releasable latching means (118) cooperating between saidboxlike structure and said tilting structure (110) for normallymaintaining the tilting structure in a fixed and rigid relationship withrespect to the boxlike structure; an air recirculation system (14)provided on said housing and coupled to said drying chamber (24) forsupplying dry pressurized air into the drying chamber and removing wetair from the drying chamber, said air circulation system including anair discharge opening (49) adjacent a lower rear portion of said chamber(24) for direct communication with the air supply opening (95) definedin the rear wall of the hopper; said housing also defining therein aclosed wet air chamber (32) which functions as part of the airrecirculation system for receiving therein the wet air returned from thedrying chamber (24); and said system also including refrigeration meanshaving an evaporator (34) and a main condenser (38) positioned withinsaid wet air chamber (32) for condensing the moisture from the airrespectively.
 6. An apparatus according to claim 5, wherein said wet airchamber (32) has an inlet (35) at one end thereof which communicatesdirectly with the drying chamber (24) for permitting flow of wet airfrom the drying chamber through said inlet into said wet air chamber,said wet air chamber at the other end thereof communicating with anintake (45) to a fan unit (42) which recirculates the air through thesystem, said evaporator (34) and said condenser (38) being disposed inseries in said wet air chamber (32) so that the wet air entering saidone end thereof first flows across said evaporator (34) and then acrosssaid condenser (38) before being resupplied to said fan unit (42), andsaid refrigeration means including a refrigerant-containing heattransfer coil (57) positioned within said wet chamber (32) downstream ofsaid evaporator (34) but upstream of said condenser (38) for heattransfer contact with the air flowing through said chamber (32), saidheat transfer coil (57) having refrigerant flowing therethrough and therefrigerant inlet thereof coupled to the refrigerant outlet of theevaporator (34), whereby the air leaving the evaporator and passing overthe heat transfer coil is effective for causing cooling of therefrigerant.
 7. An apparatus according to claim 5, wherein therefrigeration means includes a secondary condenser (51) mounted on saidhousing so as to be free of contact with the recirculated air, saidsecondary condenser being exposed to ambient air, auxiliary fan means(53) for selectively moving ambient air through said secondary condenser(51) when additional cooling of the refrigerant is desired, and controlmeans (66) for sensing refrigerant pressure or temperature andactivating said auxiliary fan means (53) whenever the refrigerantpressure or temperature reaches a predetermined maximum.
 8. An apparatusaccording to claim 7, wherein said wet air chamber (32) has an inlet(35) at one end thereof which communicates directly with the dryingchamber (24) for permitting flow of wet air from the drying chamberthrough said inlet into said wet air chamber, said wet air chamber atthe other end thereof communicating with an intake (45) to a fan unit(42) which recirculates the air through the system, said evaporator (34)and said condenser (38) being disposed in series in said wet air chamber(32) so that the wet air entering said one end thereof first flowsacross said evaporator (34) and then across said condenser (38) beforebeing resupplied to said fan unit (42), and said refrigeration meansincluding a refrigerant-containing heat transfer coil (57) positionedwithin said wet chamber (32) downstream of said evaporator (34) butupstream of said condenser (38) for heat transfer contact with the airflowing through said chamber (32), said heat transfer coil (57) havingrefrigerant flowing therethrough and the refrigerant inlet thereofcoupled to the refrigerant outlet of the evaporator (34), whereby theair leaving the evaporator and passing over the heat transfer coil iseffective for causing cooling of the refrigerant.
 9. An apparatusaccording to claim 5, including control means (65) for sensing therefrigerant pressure and for shutting off the refrigeration meanscompressor (54) whenever a predetermined minimum temperature is sensedso as to permit automatic defrosting of the coil of the evaporator (34).